More than half of the winners picked up their first Ivor at the ceremony, including La Havas who won Best Album for her self-titled record, written with musician and producer Matthew Hales.
Awards presenters the Ivors Academy described it as "a stunning concept album, its song cycle depicts the stages of a relationship from early romance to its end".
"I'm really happy, I can't believe it," La Havas said.
Styles, who is currently in the US with Love on Tour, did not attend the event.
Celeste and producer Jamie Hartman won the Songwriter of the Year category for a catalogue of songs including Stop This Flame, I Can See The Change, Little Runaway, Love Is Back and A Little Love.
Adore You won the PRS for Music Most Performed Work of 2020 for Styles and fellow writers Amy Allen, Tyler Johnson and Kid Harpoon.
The Best Song Musically and Lyrically went to Nigerian music artist Obongjayar, who lives in London, and musician Barney Lister for God’s Own Children.
In the 66th iteration of the awards, Roland Orzabal and Curt Smith of Tears for Fears, known for 1980s hits such as Shout and Everybody Wants to Rule the World, were recognised in the Outstanding Song Collection category. The duo is set to release their first album in 17 years, in the coming months.
"We've been never been able to describe any albums we've done," Smith said. "All you can say is it's how we feel right now and what we feel like recording right now. It sounds like a Tears for Fears record."
Rockers Jon Bon Jovi and Richie Sambora were honoured with the Special International Award with Apple Music for their musical partnership, while electronic music duo Goldfrapp took The Ivors Inspiration Award.
Speaking to the BBC ahead of the ceremony, Sambora named Bon Jovi's 1986 single Livin' On A Prayer as his favourite track by the rock group.
"That song affected everybody planetarily almost immediately," he said. "It gave people hope and it became a big hit in 24 countries. So I'm pretty proud of that one."
Other winners included Children of the Internet which was named Best Contemporary Song. The track, written by rapper Dave and producer Fraser T Smith, addresses the impact of social media.
Shaznay Lewis, Ivor Novello Award winner and chair of The Ivors Awards Committee at The Ivors Academy, said: "I'm amazed by the impressive range of talent who have joined the UK's roll call of songwriting greats by winning an Ivor Novello Award.
"Each one brings joy to so many and creates the soundtrack to our lives. As well as being astounded by their achievements, I would like to thank every winner and nominee for creating the most wonderful and era-defining music."
US songwriter Amy Allen, who wrote Adore You with Styles, recalled working with the former One Direction star.
"I was nervous for sure for the first 10 minutes, but Harry is hysterical and I was laughing from minute one. We were dancing and laughing. We just had a great time," she told news agency PA.
The awards, named after the early 20th-century Welsh composer, actor and entertainer, were first handed out in 1956.
Among the celebrities attending the ceremony was Abba member Bjorn Ulvaeus, who has launched the Credits Due campaign for songwriters and composers to be recognised for their work.
"Credits are so important for the creators ... it's the way other people get to hear about them," he said.
"The song is as big a star as the recording and the artist. But it is treated unfairly in comparison. The song gets much less than the recording does and that is not good for the ecosystem."
Referring to young songwriters missing out, he said: "That could happen and that is happening as we speak. But it is a big and complex business and it is very hard to change anything. But it is getting there."
– Additional reporting by Reuters